(Idea proposed by Latecomer with whom this is a collaboration. Takes place after "The One Where Pinkie Pie Knows". The Sex tag is for implications of sex but no actual sexual content.)
The news that Princess Cadence is having a baby came as a surprise to all but one mare, but now the secret is out and there's lots to discuss about it. Including the fact that Cadence is going to be a mom.
At a sleepover at Twilight's castle shortly after the big announcement, the girls all start to consider whether they might one day have families of their own. This kind of curiosity naturally gets them talking as each consider their own parental styles and restrictions or barriers to being a parent.
The resulting discussions may just reveal some things about themselves that the six mares have never known before. After all, no two mares approach the aspect of motherhood in quite the same way.